The Internet address http://community.freepbx.org/t/call-forward-authorization/6089, accessible since Jul. 21, 2016 on the World Wide Web, also concerns the stated problem.
U.S. Pat. No. 6,631,187 B1 likewise addresses this problem, and offers the solution of requiring authorization from the forwarding target for valid activation of a forward. In this case, queries can be sent to the target.
However, the document does not present an effective way to accomplish this.
U.S. Pat. No. 6,442,266 B1 describes an adaptable system for forwarding telephone calls, which is dependent upon the telephone number of the calling party. It works with a timer.
The German patent application with official file number 10 2016 112 685.3, submitted before the filing date of this application but not yet published on the date of this application, translated to English under the title “Harmonizing telephony conversations involving embedded devices and social media applications,” describes a telephone terminal device with which social media and additional services, among other things, can be used and usage-related services can be called up and displayed, even when these services are operating through another terminal device, such as a personal computer. This patent application relates in particular to one aspect of the “Circuit” applet from the company Unify Software and Solutions GmbH & Co. KG. Information on this applet was released on Jul. 21, 2016 on the World Wide Web under the address https://www.circuit.com/de/home. The applet creates a “virtual meeting room” and combines services from different terminal devices so that they can be used together, such as normal (voice) telephony and video telephony, chat, e-mails, use of social networks as well as search function and storage of content in the system.